String concatenation is one of the most common, but, a pretty expensive operation. It can hit the performance severly if not used correctly. The performance goes down drastically if you append strings using ‘&’ OR ListAppend() in a loop. I have seen application performance improving by 50-100% just by optimizing String concatenation (though that depends on how much concatenation is used in the app). So what do you about it?
The simplest and the most optimized way to do these append operations is using java’s StringBuffer. (I am sure you must be aware of it but still.. 
) .
The code would look like
<cfset sb = createObject("java", "java.lang.StringBuffer")> <cfloop from=1 to=100 index=i> <cfset sb.append("something")> <cfset sb.append(i)> </cfloop> <cfset result=sb.toString()>
Sometimes I feel that we should have a datastructure like this in ColdFusion directly but again I think whats wrong with using StringBuffer? Its like any other function which we would create. Isn’t it so?
If you are a puristic and don’t want to use any java API inside your CF app, there is another simple way to do the same thing. It uses ColdFusion Array to do the same thing what StringBuffer does. Instead of appending the string in the buffer, you can append to the array using ArrayAppend() and then once you are done and want to get the string back, use ArrayToList() with empty string (”") as delimiter. The code would look like
<cfset arr = ArrayNew(1)> <cfloop from=1 to=100 index=i> <cfset ArrayAppend(arr, "something")> <cfset ArrayAppend(arr, i)> </cfloop> <cfset result=ArrayToList(arr,"")>
This would give a much better performance as compared to concatenation using ‘&’ or using ListAppend() but will have lower performance as compared to StringBuffer. That is because of the overhead of Array object creation and array append operation. ArrayToList() will anyway create the string buffer and append the strings
You should use ‘&’ or ListAppend() only when there are only 2-3 strings to be concatenated. Otherwise always use either of the two techniques above.
